An ultimate object of communication is to transmit or exchange information immediately to anyone any time from anywhere. In addition to the conventional fixed point-to-point communication, a mobile communication has been being developed gradually. Mobile communication is a communication between a moving body (including man) such as ship, automobile or aircraft and a general subscriber's station or an office and it is also a communication between moving bodies. Recently, portable telephones and cordless telephones which are mobile communication devices have been developed actively.
The reduction in size of a portable telephone is important in its use. Since a portable telephone set is used while holding the receiver to the ear, it is necessary to give consideration from a human engineering stand. This is an obstacle to the reduction in size of a portable telephone set. Therefore, it has been desired to attain the reduction of size while giving consideration from a human engineering stand. Further, since a portable telephone set is often used at a place where there is no illumination during the night, it is absolutely necessary to provide a structure having an illuminating function using back light.
In conventional portable telephone sets, a light guide plate for back light is provided separately from the case to attain an illuminating function during the night, and a switch portion is constituted by a silicone rubber switch. Since the switch portion is formed using silicone rubber, there has been the problem that the reduction in size of a portable telephone set is not attained to a satisfactory extent.
To meet the demand for the reduction of both size and weight, it is necessary to use a thin-walled telephone set, and in the interior of the case there are accommodated electronic parts which have been packaged in high density. Since in a portable telephone set there is utilized a high frequency band of 800 to 900 MHz or so called a quasi-microwave band, it is necessary to strengthen the electromagnetic shield in the interior of the case while attaining a reduction in weight of the case, thereby preventing various troubles caused by electromagnetic interference.
According to the prior art, a metallic film is formed on the inner surface of a resin molded case by, for example, plating, electrostatic coating, or vapor deposition of aluminum, and a high frequency function circuit is received therein and electromagnetic shield is performed. However, with the reduction in size and weight of portable telephone sets, it has become necessary to adopt a three-dimensional circuit configuration wherein parts are packaged to a molded case itself, and with the conventional electromagnetic shield structure it has become impossible to cope with such necessity.